The name Haas Effect is given to a physical phenomenon regarding the perception of sound by the brain. Let's consider the case of a sound generated by a single sound source and let's imagine that we are inside a room and sitting at a certain distance from the sound source. Because of the reflections of sound against the walls we will first of all be reached by the signal that comes directly from the sound source and therefter by the signal's reflections bouncing off the walls. This delay is because the reflected sound has a longer way to go to reach the listener compared to the direct signal. If the two signals arrive with a slight delay one from the other it is perceived by the brain as a single sound coming from one sole direction. The direction identified by the brain as being that of the sound source is the one belonging to the signal that reaches the ears first (this is true even if the second wave's intensity is greater than the first wave's) and for this reason the effect is labelled precedence effect. This effect takes place when the delay between two signals is sufficiently small, to be precise it must be less than 30-35 ms. This time interval is called the Haas zone:
Equation 2.2. The Haas Zone
[0 - 35ms]
When the delay between the signals steps out of the bounds of the Haas Zone we perceive two distinct signals and we enter the domain of the Echoe Effect, in which the listener perceives two sounds as being distinct. The Haas Effect is utilized in sound reinforcement systems on signals sent to delay towers [Sound reinforcement ] .
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